Electrophotographic printers with detachably mountable developing cartridges are well known in the art. The developing cartridge is provided with an outer case rotatably supporting a developing roller that serves to carry toner on the surface thereof; a thickness-regulating blade regulating a thickness of a layer of toner carried on the developing roller; and side seals designed to prevent toner from leaking out of axial ends of the outer case with respect to an axial direction of the developing roller.
As one of such conventional developing cartridge, there is proposed a developer cartridge whose thickness-regulating blade is configured of a leaf spring member, and a rubber pressing member disposed on the leaf spring member for contacting a peripheral surface of a developing roller with pressure. Each side seal includes a sponge seal member affixed to an outer case, and a felt seal member layered over the sponge seal member. The felt seal members contact the peripheral surface of the developing roller and slide over the peripheral surface as the developing roller rotates.
With this conventional developer cartridge, an upper end of each sponge seal member is interposed between a lower end of the leaf spring member and the outer case. The felt seal member extends from the lower end of the leaf spring member across the sponge seal member to a bottom end of the outer case and is affixed thereto.